Laminate structures with hole plugs and methods of forming laminate structures with hole plugs

ABSTRACT

Laminate structures including hole plugs, and methods for forming a hole plug in a laminate structure are provided. A laminate structure may be formed with at least a dielectric layer and a first conductive foil on a first side of the dielectric layer. A blind hole may be formed in the laminate structure extending toward the first conductive foil from a second side of the dielectric layer and at least partially through the dielectric layer, the blind hole including a hole depth to hole diameter aspect ratio of less than ten (10) to one (1). Via fill ink may be disposed in the blind hole, and the via fill ink may be dried and/or cured to form a hole plug.

CLAIM OF PRIORITY

The present application is a divisional application of U.S. patent application Ser. No. 14/998,135, filed Dec. 23, 2015, which claims priority to U.S. Provisional App. Ser. No. 62/096,011, filed Dec. 23, 2014, U.S. Provisional App. Ser. No. 62/096,817, filed Dec. 24, 2014, and U.S. Provisional App. Ser. No. 62/128,958 filed Mar. 5, 2015.

FIELD

Various features relate to laminate structures, and more particularly, to thin laminate structures with hole plugs, and methods of forming laminate structures with hole plugs.

BACKGROUND

Laminate structures, such as printed circuit boards, are typically prepared by first laminating a sub-composite structure with additional exterior sheets/layers and/or other sub-composite structures. One or more holes may be formed (e.g. drilled) within the sub-composite for via holes. When laminates get thinner and holes get larger in diameter, using traditional hole filling materials and processes are inadequate.

Consequently, what is needed a way to create hole plugs in thin laminate structures in an efficient and cost effective way.

SUMMARY

Various aspects of the disclosure facilitate hole plugs in thin laminate structures. According to at least one aspect, methods for forming a hole plug in a laminate structure are disclosed. In one or more examples, such methods may include forming a laminate structure including at least a dielectric layer and a first conductive foil on a first side of the dielectric layer. The dielectric layer further includes a second side opposite from the first side by a thickness of the dielectric layer. A blind hole with a trimmed bottom corner may be formed in the laminate structure, extending from the second side of the dielectric layer toward the first conductive foil. In some examples, the blind hole may include a hole depth to hole diameter aspect ratio of less than twenty (20) to one (1). In some examples, via fill ink may be deposited in the blind hole, and the via fill ink may be dried and/or cured to form a hole plug.

Additional aspects of the present disclosure include laminate structures. According to at least one example, such a laminate structure may include a dielectric layer with a first side and an opposing second side separate from the first side by a thickness of the dielectric layer. A first conductive foil may be disposed on the first side of the dielectric layer. A blind hole may be formed in the dielectric layer extending through the dielectric layer from the second side of the dielectric layer toward the first conductive foil without piercing the first conductive foil. The bind hole may include a trimmed bottom corner and a hole depth to hole diameter aspect ratio of less than twenty (20) to one (1). A via fill ink may be disposed in the blind hole to form a hole plug.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-section view of the construction of an unpierced laminate structure having a filled via hole.

FIG. 2 is a flow diagram illustrating a method for forming an unpierced thin laminate structure with a hole plug.

FIG. 3 illustrates a cross-section view of the construction of an unpierced laminate structure having a laser-drilled filled via hole.

FIG. 4 is a flow diagram illustrating a method for forming a thin laminate structure with a hole plug.

FIG. 5 illustrates an exemplary drill that may be used to for a hole in accordance with FIGS. 1 and 2.

DETAILED DESCRIPTION

In the following description, specific details are given to provide a thorough understanding of the various aspects of the disclosure. However, it will be understood by one of ordinary skill in the art that the aspects may be practiced without these specific details. For example, circuits may be shown in block diagrams in order to avoid obscuring the aspects in unnecessary detail. In other instances, well-known circuits, structures and techniques may not be shown in detail in order not to obscure the aspects of the disclosure.

The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any implementation or aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects of the disclosure. Likewise, the term “aspects” does not require that all aspects of the disclosure include the discussed feature, advantage or mode of operation.

Exemplary Unpierced Thin Laminate Structure with a Filled Via Hole

FIG. 1 illustrates a cross-section view of the construction of an unpierced laminate structure 100 having a filled via hole. At a first stage (Stage A), the laminate structure 100 may be formed by including a dielectric layer 102 sandwiched between a first conductive layer or foil 106 (e.g., cooper foil) and/or a second conductive layer or foil 104. While a double sided laminate 100 is illustrated, a single sided laminate (i.e., one dielectric layer and one conductive layer or foil) and/or unclad laminate are also contemplated to be used. In one example, the first conductive layer or foil 106 and a second conductive layer or foil 104 may be selected from commonly available copper foil thickness, for example, approximately between 12 oz (approx. 420 micron thick or less) and 3 micron thick or less. In one example, the dielectric layer 102 may have a thickness of 20 mil or less.

At a second stage (Stage B), a drill 108 may be used to form an unpierced or blind hole 110 through the second conductive layer or foil 104 and the dielectric layer 102, but not drill through or only partially drill through the first conductive layer or foil 106. In order to make the unpierced or blind hole 110 through at least the second conductive layer or foil 104 without piercing the first conductive layer or foil 106, the drill point angle may be equal to or greater than 125 degrees. Alternatively, the drilling machine used may have a depth sensor from the surface of the laminate structure 100 or drill depth. In yet another implementation, the drill machine may have sensors to sense when the drill contacts the first and/or the second conductive layer or foil.

At a third stage (Stage C), the hole 110 has been formed within the unpierced laminate structure 100. Note that because a thin laminate 100 is used, the aspect ratio of the hole depth to the hole diameter may be 10:1 or less, 5:1 or less, 4:1 or less, 3:1 or less, 2:1 or less, 1:1 or less, 1:2 or less, 1:3 or less, or 1:10 or less. For example, if the hole depth may be 100 microns deep and the hole diameter may be 1 millimeter wide, then the aspect ratio (i.e., hole depth to hole diameter ratio) may be 1:10 or 0.1. Conventional via fill ink and hole filler machines are designed to work with through holes having aspect ratios of 5:1 or higher.

At a fourth stage (Stage D) a via fill ink 112 (or other similarly via fill material of similar viscosity) is deposited into the hole 110 using a hole filler machine. In one example, the hole filler machine may be feature a vacuum assisted process to prevent bubbles in the via fill ink. Once inserted in the hole 110, the via fill ink 112 may form a hole plug. In one example, the via fill ink 112 may be a plating resist material. According to various approaches, the via fill ink 112 may be deposited in the hole 110 by screen or stencil printing, by an ink dispenser, by a squeezing in on the surface and these process may be assisted by vacuum. In some implementations, the via formed on the surface of the laminate substrate 100 may be prepared with a disposable layer, so that after the via fill ink is deposited in the hole 110, the disposable layer can be removed to clean the surface of the laminate structure 100.

Because of the low aspect ratio of the hole depth to the hole diameter (e.g., aspect ratio of 10:1 or less, 5:1 or less, 4:1 or less, 3:1 or less, 2:1 or less, 1:1 or less, 1:2 or less, or 1:10 or less). It should be noted that conventional via fill material may not properly fill the hole 110 and a conventional filler machine may be a cause for bubbles in the hole plug. In the proposed approach, a proper viscosity and thixotropic property prepared via fill ink is used that allows it to flow in and fill the hole 110. In various examples, the via fill ink 112 may have a viscosity of 100-10000 deciPascal-second (dps-s) at 25 degrees Celsius, 200-1000 deciPascal-second (dps-s) at 25 degrees Celsius, and/or 200-500 deciPascal-second (dps-s) at 25 degrees Celsius, etc. The thixotropic index, the ratio of static viscosity to dynamic viscosity may be 2 or greater, preferably 3 or greater. In some implementations, the via fill ink 112 may also be screen printable, stencil printable, and/or squeeze fillable. The ink filler machine may feature vacuum assist and/or a heater to prevent bubbles in the ink.

During a subsequent plating process, if the via fill ink is a plating resist material, the via fill ink 112 may prevent conductive material from being plated between the first conductive layer or foil 106 and the second conductive layer or foil 104.

The via fill ink 112 may be cured or semi-cured. A vacuum dry process may be applied prior to via fill ink 112 heat cure process. Heat may be applied during vacuum dry to assist via fill ink debubbling. For example, the via fill ink made with a solvent 112 may be vacuum dried. In one example, the vacuum drying conditions may be a pressure of 360 millimeters of mercury (mmHg) or less, or 150 mmHg or less, for a length of time greater than 30 seconds at a set pressure or greater than 90 seconds at the set pressure. Or heat may be applied to the via fill ink for curing. Vacuum and heat curing processes may be performed simultaneously to perform debubbling and cure of the via fill ink.

At an optional fifth stage (Stage E), the laminate structure 100 may be added or laminated onto additional layers 120 and 122, such as one or more core structure and/or additional laminate structures with prepreg, on either one side or both sides of the laminate structure 100 to form a multilayer structure 130. In one example, the additional laminate structures may include dielectric and conductive layers or foils. The conductive layers (e.g., conductive foils) may be patterned to form electrical paths or traces.

At an optional sixth stage (Stage F), a through-hole 124 may be drilled through the multilayer structure 130, including through the via fill ink 112. The through-hole 124 may have a diameter smaller than the diameter of the first formed hole 110 and or the via fill ink 112. The through-hole 124 may then be plated, for example, by placing the panel into a seed bath, followed by immersion in an electroless copper bath, followed by electrolytic plating.

FIG. 2 is a flow diagram illustrating a method for forming an unpierced thin laminate structure with a via fill hole plug. A laminate structure is formed including at least a dielectric layer and a first conductive foil on a first side of the dielectric layer 202.

An unpierced or blind hole is formed in the laminate structure extending toward the first conductive foil and at least partially through the dielectric layer, the hole having a hole depth to hole diameter aspect ratio of less than ten (10) to one (1) 204. The aspect ratio (i.e., hole depth to hole diameter) may be, for example, 10:1 or less, 5:1 or less, 4:1 or less, 3:1 or less, 2:1 or less, 1:1 or less, 1:2 or less, or 1:10 or less. In one example, a drill is used to form the hole, the drill having a point angle equal or greater than 125 degrees or more or 155 degrees or more. Via fill ink may then be deposited in the hole 206. The via fill ink may be dried and/or cured to form a hole plug 208. A plated through hole may be subsequently formed through the hole plugged material. The hole plug may be a plating resist or a material that prevents metal plating.

Additionally, the laminate structure may further include a second conductive foil on the second side of the dielectric layer, wherein the second conductive foil is pierced by the hole. In one example, the laminate structure may further include a disposable layer on the second conductive foil. In one implementation, a multilayer printed circuit board may be formed with the laminate structure.

In one implementation, the hole may be formed with a drill having a point angle equal or greater than 125 degrees. Alternatively, the hole may be formed with a drill having a point angle equal or greater than 155 degrees. The drill may be configured to form a trimmed bottom corner within the hole.

In one example, the via fill ink may be deposited by at least one of: (a) screen printing, (b) stencil printing, or (c) squeezing the via fill ink into the hole.

In some implementations, the via fill ink deposition may be assisted by vacuum (e.g., in a vacuum chamber), to debbubble the via fill ink (i.e., remove bubbles from the via fill ink).

The drying and/or curing of the via fill ink may be done, for example, within an oven.

In one example, thermal cure process is simultaneously proceeded.

In various implementations, the first conductive foil may have a thickness of 12 ounce or less, 2 ounce or less, or 1 ounce (oz) or less.

In some implementations, the dielectric layer may have a thickness of 20 mil or less, 16 mil or less, or 12 mil or less.

Exemplary Unpierced Thin Laminate Structure with a Laser-Drilled Filled Via Hole

FIG. 3 illustrates a cross-section view of the construction of an unpierced laminate structure 300 having a laser-drilled filled via hole. At a first stage (Stage A), the laminate structure 300 may be formed by including a dielectric layer 302 sandwiched between a first conductive layer or foil 306 (e.g., cooper foil) and/or a second conductive layer or foil 304. While a double sided laminate 300 is illustrated, a single sided laminate (i.e., one dielectric layer and one conductive layer or foil) and/or unclad laminate are also contemplated to be used. In one example, the first conductive layer or foil 306 and a second conductive layer or foil 304 may be selected from commonly available copper foil thickness, for example, approximately 12 oz (420 micron) thick or less, 2 oz (70 micron) thick or less, or 1 oz (35 micron) thick or less. In one example, the dielectric layer 302 may have a thickness of 20 mil or less (e.g., 16 mil or less, 12 mil or less, 8 mil or less).

At a second stage (Stage B), a conformal mask formation process may be achieved by etching process of chemical etchant or laser abrasion to form an opening 308 on the second conductive layer or foil 304 which exposes the dielectric layer 302.

At a third stage (Stage C), laser drilling may be used to form an unpierced or blind hole 310 through the dielectric layer 302 of the laminate structure 300. In some examples, the laser may be a CO2 laser, a UV laser, or a complex CO2 and UV laser. If the laser aperture is not sufficient for the hole size, a common trepanning method may be used. The laser drill will be stopped by adjacent copper foil and it makes the hole is unpierced or blind.

At a fourth stage (Stage D) a via fill ink 312 (or other similarly via fill material of similar viscosity) is deposited into the hole 310 using a hole filler machine. In one example, the hole filler machine may be featured vacuum assisted process to prevent bubbles in the via fill ink. Once inserted in the hole 310, the via fill ink 312 may form a hole plug. In one example, the via fill ink 312 may be a plating resist material. According to various approaches, the via fill ink 312 may be deposited in the hole 310 by screen or stencil printing, by an ink dispenser, by a squeezing in on the surface and these process may be assisted by use of a vacuum. In some implementations, the surface of the laminate substrate 300 through which the via is formed may be prepared with a disposable layer, so that after the via fill ink 312 is deposited in the hole 310, the disposable layer can be removed to clean the surface of the laminate structure 300.

Because of the low aspect ratio of the hole depth to the hole diameter (e.g., aspect ratio of 10:1 or less, 5:1 or less, 4:1 or less, 3:1 or less, 2:1 or less, 1:1 or less, 1:2 or less, 1:10 or less), conventional via fill materials and/or processes do not work well.

It should be noted that conventional/thicker via fill material may not properly fill the hole 310 and a conventional filler machine may be a cause for bubbles in the hole plug. Here, a proper viscosity and thixotropic property prepared via fill ink is used that allows it to flow in and fill the hole 310. In various examples, the via fill ink 312 may have a viscosity of 100-10000 deciPascal-second (dps-s) at 25 degrees Celsius, 200-1000 deciPascal-second (dps-s) at 25 degrees Celsius, and/or 200-500 deciPascal-second (dps-s) at 25 degrees Celsius, etc. In some implementations, the via fill ink 312 may also be screen printable, stencil printable, and/or squeeze fillable. The ink filler machine may feature vacuum assist and/or heater to prevent bubbles in the ink.

During a subsequent plating process, if the via fill ink is a plating resist material, the void fill ink 312 may prevent conductive material from being plated between the second conductive layer or foil 304 and the first conductive layer or foil 306.

The via fill ink 312 may then be cured or semi-cured. Vacuum dry process may be applied prior to via fill ink 312 heat cure process. Heat may be applied during vacuum dry to assist via fill ink debubbling. For example, the via fill ink 312 may be vacuum dried. In one example, the vacuum drying conditions may be a pressure of 360 millimeters of mercury (mmHg) or less, or 150 mmHg or less, for a length of time greater than 30 seconds at a set pressure or greater than 90 seconds at the set pressure. The via fill ink may be applied heat for further cure. Vacuum dry and heat cure process may be proceeded simultaneously.

At an optional fifth stage (Stage E), the laminate structure 300 may be added or laminated onto additional layers 320 and 322, such as a core structure and/or additional laminate structures, on either one side or both sides of the laminate structure 300 to form a multilayer structure 330. In one example, the additional laminate structures may include dielectric and conductive layers or foils. The conductive layers (e.g., conductive foils) may be patterned to form electrical paths or traces.

At an optional sixth stage (Stage F), a through-hole 324 may be drilled through the multilayer structure 330, including through the via fill ink 312. The through-hole 324 may have a diameter smaller than the diameter of the first formed hole 310 and or the via fill ink 312. In one example, the through-hole 324 may then be plated, for example, by placing the panel into a seed bath, followed by immersion in an electroless copper bath, followed by electrolytic plating.

FIG. 4 is a flow diagram illustrating a method for forming a thin laminate structure with a filled hole plug. A laminate structure is formed including a dielectric layer, a first conductive foil on a first side of the dielectric layer, and a second conductive foil on a second side of the dielectric layer 402. The second conductive foil may then be partially removed (e.g., masked and etched) to form an opening on the second conductive foil that exposes a portion of the dielectric layer 404. The exposed portion of the laminate structure may then be laser drilled to form an unpierced or blind hole extending toward the first conductive foil and at least partially through the dielectric layer, the hole having a hole depth to hole diameter aspect ratio of less than ten (10) to one (1) 406. Via fill ink may then be deposited in the hole 408 and cured to form a hole plug 410. The second conductive foil is pierced by the hole. A plated through hole may be formed through the hole plugged material. The hole plug may be a plating resist or a material that prevents metal plating.

Additionally, the laminate structure may further include a disposable layer on the second conductive foil. In one example, a multilayer printed circuit board may be formed with the laminate structure.

In various examples, the hole aspect ratio (via hole depth to diameter ratio) may be, for instance, ten (10) to one (1) or less, five (5) to one (1) or less, four (4) to one (1) or less, three (3) to one (1) or less, or two (2) to one or less, or one (1) to one (1) or less, or one (1) to two (2) or less. In other implementations, the hole aspect ratio (via hole depth to diameter ratio) may be, for instance, between ten (10) to one (1) and one (1) to one (1), between ten (10) to one (1) and one (1) to one (1), between five (5) to one (1) and one (1) to one (1), between four (4) to one (1) and one (1) to one (1), between three (3) to one (1) and one (1) to two (2), or between two (2) to one (1) and one (1) to one (1) or one (1) to two (2). In various implementations, the via fill ink may be deposited by at least one of: (a) screen printing, (b) stencil printing, and (c) squeezing the via fill ink into the hole.

In some implementations, the via fill ink deposition may be assisted by vacuum (e.g., done within a vacuum chamber) to debubble the via fill ink (i.e., to remove bubbles from the via fill ink).

In one example, the via fill ink may be cured within an oven. The thermal cure process may be simultaneously proceeded.

In various examples, each of the first conductive foil and second conductive foils may have a thickness of 12 ounce or less, 2 ounce or less, or 1 ounce or less.

In other examples, the dielectric layer has a thickness of 20 mil or less, 16 mil or less, or 12 mil or less.

Exemplary Drill for Hole Formation

FIG. 5 illustrates an exemplary drill that may be used to for a hole in accordance with FIGS. 1 and 2. Here a laminate structure 502 (e.g., comprising a dielectric layer and no conductive layers, or a dielectric layer and one or more conductive layers or foils) may have a hole formed by a drill 504 that is shaped or configured to form a trimmed bottom corner within the hole. The trimmed bottom corner minimize potential bubble trap. For example, the drill may have a point angle β equal or greater than 125 degrees or a point angle β equal or greater than 155 degrees. Because the hole depth may be rather shallow (relative to the hole diameter), such drill point angle may be necessary to form a hole capable of accepting the via fill ink.

Note that the aspects of the present disclosure may be described herein as a process that is depicted as a flowchart, a flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. A process is terminated when its operations are completed. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination corresponds to a return of the function to the calling function or the main function.

The various features of the disclosure described herein can be implemented in different systems and devices without departing from the disclosure. It should be noted that the foregoing aspects of the disclosure are merely examples and are not to be construed as limiting the disclosure. The description of the aspects of the present disclosure is intended to be illustrative, and not to limit the scope of the claims. As such, the present teachings can be readily applied to other types of apparatuses and many alternatives, modifications, and variations will be apparent to those skilled in the art. 

What is claimed is:
 1. A method for forming a hole plug, comprising: forming a laminate structure including at least a dielectric layer and a first conductive foil on a first side of the dielectric layer, the dielectric layer including a second side opposite from the first side by a thickness of the dielectric layer; forming a blind hole with a bottom surface, a sidewall substantially transverse to the bottom surface, and a trimmed bottom corner in the laminate structure, the blind hole extending through the dielectric layer toward the first conductive foil from the second side of the dielectric layer, the blind hole including a hole depth to hole diameter aspect ratio of less than twenty (20) to one (1); disposing via fill ink in the blind hole; and drying and/or curing the via fill ink to form a hole plug.
 2. The method of claim 1, further comprising: forming the laminate structure to further include a second conductive foil on the second side of the dielectric layer, wherein the second conductive foil is pierced by the blind hole.
 3. The method of claim 1, further comprising: incorporating the laminate structure into a multilayer printed circuit board.
 4. The method of claim 1, further comprising: forming a plated through hole through the hole plug.
 5. The method of claim 1, wherein forming the blind hole with the trimmed bottom corner comprises: forming the blind hole with a drill having a point angle equal or greater than: (a) 125 degrees, or (b) 155 degrees.
 6. The method of claim 1, wherein depositing the via fill ink comprises depositing the via fill ink with vacuum assistance.
 7. The method of claim 1, wherein the first conductive foil has a thickness of 12 ounce or less, 2 ounce or less, or 1 ounce or less.
 8. The method of claim 1, wherein the dielectric layer has a thickness of 20 mil or less, 16 mil or less, or 12 mil or less.
 9. The method of claim 1, wherein the via fill ink comprises a plating resist or a material that prevents metal plating.
 10. A laminate structure, comprising: a dielectric layer including a first side and an opposing second side separate from the first side by a thickness of the dielectric layer; a first conductive foil disposed on the first side of the dielectric layer; a blind hole in the dielectric layer extending through the dielectric layer from the second side of the dielectric layer toward the first conductive foil without piercing the first conductive foil, the bind hole including a bottom surface, a sidewall substantially transverse to the bottom surface, and a trimmed bottom corner and a hole depth to hole diameter aspect ratio of less than twenty (20) to one (1); and via fill ink disposed in the blind hole to form a hole plug.
 11. The laminate structure of claim 10, further comprising: a second conductive foil on the second side of the dielectric layer, wherein the second conductive foil is pierced by the blind hole.
 12. The laminate structure of claim 10, further comprising: a plated through hole through the hole plugged material.
 13. The laminate structure of claim 10, wherein the trimmed bottom corner of the blind hole comprises a point angle equal or greater than: (a) 125 degrees, or (b) 155 degrees.
 14. A multilayer printed circuit board comprising the laminate structure of claim
 10. 